Solve the login problem of Webmin in Centos

The problem is I can not sign in the Webmin panel. I did a lot of searches and finally got the solution.

Here is the situation:

Oracle VM Free Tier. I selected the Image: CentOS-7-2020.04.21-0.
For CentOS, SSH public key connection. The user is OPC when I try to ssh to it.
Then I add a new user and add it to the group wheel. the username is admin.
Based on the How To Create a Sudo User on CentOS on DigitalOcean.
I followed the installation guide on the Webmin support page. The ports 10000 to 10010 are opened.
In the browser, I can see the login page. But can not log in with the new user, admin.
Check the error log of webmin at /var/webmin/miniserv.error
The error message is missing Perl module Authen::PAM
Then I install Authen::PAM in the ssh window.
Try to login again. Still can not log in.
I restart the server, and still can not log in.

/usr/libexec/webmin/changepass.pl /etc/webmin username password

Replace username by root, and with my own password.

After this command, I can log in the Webmin as root.

See the basic information of this VM.

Features: